// Because the memory map is so important to not be aliased, it is defined here, in one place
// The lower 256 PML4 entries are reserved for userspace
// Each PML4 entry references up to 512 GB of memory
// The top (511) PML4 is reserved for recursive mapping
// The second from the top (510) PML4 is reserved for the kernel
    /// The size of a single PML4
    pub const PML4_SIZE: usize = 0x0000_0080_0000_0000;
    pub const PML4_MASK: usize = 0x0000_ff80_0000_0000;

    /// Offset of recursive paging
    pub const RECURSIVE_PAGE_OFFSET: usize = (-(PML4_SIZE as isize)) as usize;
    pub const RECURSIVE_PAGE_PML4: usize = (RECURSIVE_PAGE_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset of kernel
    pub const KERNEL_OFFSET: usize = 0xFFFF_8000_0000_0000; //TODO: better calculation
    pub const KERNEL_PML4: usize = (KERNEL_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to kernel heap
    pub const KERNEL_HEAP_OFFSET: usize = RECURSIVE_PAGE_OFFSET - PML4_SIZE;
    pub const KERNEL_HEAP_PML4: usize = (KERNEL_HEAP_OFFSET & PML4_MASK)/PML4_SIZE;
    /// Size of kernel heap
    pub const KERNEL_HEAP_SIZE: usize = 1 * 1024 * 1024; // 1 MB

    /// Offset to kernel percpu variables
    //TODO: Use 64-bit fs offset to enable this pub const KERNEL_PERCPU_OFFSET: usize = KERNEL_HEAP_OFFSET - PML4_SIZE;
    pub const KERNEL_PERCPU_OFFSET: usize = 0xC000_0000;
    /// Size of kernel percpu variables
    pub const KERNEL_PERCPU_SIZE: usize = 64 * 1024; // 64 KB

    /// Offset to user image
    pub const USER_OFFSET: usize = 0;
    pub const USER_PML4: usize = (USER_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user TCB
    /// Each process has 4096 bytes, at an offset of 4096 * PID
    pub const USER_TCB_OFFSET: usize = 0xB000_0000;

    /// Offset to user arguments
    pub const USER_ARG_OFFSET: usize = USER_OFFSET + PML4_SIZE/2;

    /// Offset to user heap
    pub const USER_HEAP_OFFSET: usize = USER_OFFSET + PML4_SIZE;
    pub const USER_HEAP_PML4: usize = (USER_HEAP_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user grants
    pub const USER_GRANT_OFFSET: usize = USER_HEAP_OFFSET + PML4_SIZE;
    pub const USER_GRANT_PML4: usize = (USER_GRANT_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user stack
    pub const USER_STACK_OFFSET: usize = USER_GRANT_OFFSET + PML4_SIZE;
    pub const USER_STACK_PML4: usize = (USER_STACK_OFFSET & PML4_MASK)/PML4_SIZE;
    /// Size of user stack
    pub const USER_STACK_SIZE: usize = 1024 * 1024; // 1 MB

    /// Offset to user sigstack
    pub const USER_SIGSTACK_OFFSET: usize = USER_STACK_OFFSET + PML4_SIZE;
    pub const USER_SIGSTACK_PML4: usize = (USER_SIGSTACK_OFFSET & PML4_MASK)/PML4_SIZE;
    /// Size of user sigstack
    pub const USER_SIGSTACK_SIZE: usize = 256 * 1024; // 256 KB

    /// Offset to user TLS
    pub const USER_TLS_OFFSET: usize = USER_SIGSTACK_OFFSET + PML4_SIZE;
    pub const USER_TLS_PML4: usize = (USER_TLS_OFFSET & PML4_MASK)/PML4_SIZE;
    // Maximum TLS allocated to each PID, should be approximately 8 MB
    pub const USER_TLS_SIZE: usize = PML4_SIZE / 65536;

    /// Offset to user temporary image (used when cloning)
    pub const USER_TMP_OFFSET: usize = USER_TLS_OFFSET + PML4_SIZE;
    pub const USER_TMP_PML4: usize = (USER_TMP_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user temporary heap (used when cloning)
    pub const USER_TMP_HEAP_OFFSET: usize = USER_TMP_OFFSET + PML4_SIZE;
    pub const USER_TMP_HEAP_PML4: usize = (USER_TMP_HEAP_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user temporary page for grants
    pub const USER_TMP_GRANT_OFFSET: usize = USER_TMP_HEAP_OFFSET + PML4_SIZE;
    pub const USER_TMP_GRANT_PML4: usize = (USER_TMP_GRANT_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user temporary stack (used when cloning)
    pub const USER_TMP_STACK_OFFSET: usize = USER_TMP_GRANT_OFFSET + PML4_SIZE;
    pub const USER_TMP_STACK_PML4: usize = (USER_TMP_STACK_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user temporary sigstack (used when cloning)
    pub const USER_TMP_SIGSTACK_OFFSET: usize = USER_TMP_STACK_OFFSET + PML4_SIZE;
    pub const USER_TMP_SIGSTACK_PML4: usize = (USER_TMP_SIGSTACK_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset to user temporary tls (used when cloning)
    pub const USER_TMP_TLS_OFFSET: usize = USER_TMP_SIGSTACK_OFFSET + PML4_SIZE;
    pub const USER_TMP_TLS_PML4: usize = (USER_TMP_TLS_OFFSET & PML4_MASK)/PML4_SIZE;

    /// Offset for usage in other temporary pages
    pub const USER_TMP_MISC_OFFSET: usize = USER_TMP_TLS_OFFSET + PML4_SIZE;
    pub const USER_TMP_MISC_PML4: usize = (USER_TMP_MISC_OFFSET & PML4_MASK)/PML4_SIZE;
